Electrolytic process for making phosphine



May 17, 1966 G. T. MILLER Filed March 4, 1963 4 Sheets-Sheet l May 17,1966 G. T. MILLER ELECTROLYTIC PROCESS FOR MAKING PHOSPHINE 4Sheets-Sheet 2 Filed March 4, 1963 NQQQQQQQh 3 NQQQQQQQM May 17, 1966 G.T. MILLER ELECTROLYTIC PROCESS FOR MAKING PHOSPHINE 4 Sheets-Sheet 5Filed March 4, 1963 May 17, 1966 e. T. MILLER ELECTROLYTIC PROCESS FORMAKING PHOSPHINE 4 Sheets-Sheet 4 Filed March 4, 1963 United StatesPatent M 3,251,756 ELECTROLYTIC PROCESS FOR MAKING PHOSPI-IINE George T.Miller, Lewiston, N.Y., assignor to Hooker Chemical Corporation, NiagaraFalls, N.Y., a corporation of New York Filed Mar. 4, 1963, Ser. No.262,497 4 Claims. (Cl. 204101) This invention relates to an electrolyticcell and a 'process whereby a reactive material in such a cell reactsmore efliciently at an electrode, with a product produced thereelectrolytically, to yield a desired end product.

Electrolytic cells have been utilized to produce phosphine. In suchcells, employing phophorus as a reactive material, phosphine isrecovered in the catholyte gas. However, after operation for a period oftime, the yield of phosphine in the catholyte gas gradually diminishes,due to spongy deposits that form on the surface of the cathode as thereactions in the cell progress. The concentration of phosphine in thecatholyte gas decreases as the size of and area covered by these spongycoatings or deposits increase. The spongy coatings appear to be formedby deposits of metallic ions, from either the electrolyte or thephosphorus, usually at or near the cathode.

Although the description of the apparatus of the invention is directedto its preferred embodiment, that of an electrolytic cell which producesphosphine, it is to be understood that the apparatus may also beutilized when a reactive material is to be reacted with a product ofelectrolysis to produce a desired end product.

In accordance with the invention it has been found that a spongy mass ishindered from forming on the electrode in an electrolytic cellcomprising an electrode having a plurality of sharp edges by which thereactive material is caused to wick up the electrode, and an electrolytefrom which a product of electrolysis is generated at the electrode, thereactive material being so located as to react with the product ofelectrolysis in the vicinity of the electrode, a second electrode inoperative relationship with the electrode, the electrolyte in operativerelationship with the electrode, and second electrode and means forcausing an electrical current to flow between the electrode and secondelectrode through the electrolyte to electrolyze it and produce amaterial with which the reactive material reacts. Preferably there isalso present a diaphragm in between the electrode and second electrodeto separate the gases evolved.

The invention and modifications thereof are shown by the accompanyingdrawings, in which:

FIGURE 1 is a central sectional view in elevation of an electrolyticcell taken along plane 11 of FIGUR-E.2.

FIGURE 2 is a horizontal sectional view taken along plane 22 of FIGURE1.

FIGURE 3 is an isometric .view of a preferred contact electrode of theinvention, with the grooves being exaggerated for clear illustration.

FIGURES 4-12 are isometric views illustrating correspondingmodifications in the contact electrode of the invention.

The terms wicking and wicking up are used throughout the description todescribe the phenomenon in which molten reactive material, e.g.,phosphorus, in contact with the lower portion of a vertical electrodesurface rises above the level of the molten pool thereof to form a thinlayer on the surface of the electrode.

A description of the drawings is as follows:

Referring to FIGURE 1, there is shown a cell vessel having an anodecompartment 12, containing an anode 14, and a cathode compartment 16,containing a contact electrode (cathode) 18 having a plurality of edges46 and Patented May 17, 1966 grooves 48, as seen in FIGURE 2. A porousdiaphragm 20, separates the anode compartment 12 and the cathodecompartment 16 and separates the electrolyte into anolyte 17 andcatholyte 19 sections. In the cathode compart-ment 16 is reactivematerial 24, e.g., phophorus, in a liquid state. Diaphragm 20 iscovered, coated or protected in such a manner that the side thereoffacing the reactive material, where it may otherwise contact thatmaterial is coated with a coating, cover or sheath 22 against which thereactive material then does not adhere or wet. This action is evidencedby convex meniscus 21. Ports 2 6 and 28 permit the addition and removalof anolyte 17 from the anode section 12. Ports 30 and 32 permitthe'addition and removal of catholyte 19 from the cathode section 16.Port 34 permits the addition and removal of molten phosphorus fromcathode section 16'. Suflicient molten yellow phosphorus 24 is added tothe cathode compartment 16, to contact the lower edge of the contactelectrode 18, thereby permitting wicking up of the molten phosphorusonto the outer surface of the cathode. Anolyte gas discharge port 36 isprovided in' the top of the anode section to remove anolyte gas from theelectrolytic cell. Catholyte discharge port 38 is provided in the top ofcathode section 14 to remove catholyte gas. The level of the anolyte andcatholyte in the electrolytic cell is indicated as interface 15.

Anode electrolytical wire connector 40 and cathode electrolytical wireconnector 42 are connected to the anode and cathode and to the positiveand negative poles, through plugs 41' and 43, respectively, of a sourceof direct current 44. If desired, a heating source such as a constanttemperature hath (not shown in the drawing), may be employed to maintainthe catholyte and anolyte at a desired temperature.

Cell vessel 10 may be constructed of material capable of resistingcorrosion by the electrolyte and other materials employed in the cell.Typical examples of suitable materials of construction for cell vessel10 include glass,

glazed ceramics, tantalum, titanium, hard rubber, polyethylene, rigidmaterials coated with phenol-formaldehyde resin, and the like.

Diaphragm 20 which separates the anode section 12 I from cathode section16, may be a porous or semipermeable material resistant to the cellcontents and capable of maintaining anode and cathode gases separate.Typical examples of suitable materials for use as a diaphragm includeporous alundnm, porous porcelain, sintered glass, glass fabric, resinimpregnated W001, W001 felt, and diaphragms normally employed in leadstorage batteries.

Any solid material having a hydrogen over voltage, as normally measuredin the absence of the reactive material, e.g., phosphorus, or anymaterial exceeding the hydrogen over voltage of smooth platinum may beemployed as a cathode. Typical cathodic materials include lead, leadmercury, amalgam, cadmium, tin, aluminum, nickel, alloys of nickel, suchas Mumetal (an alloy containing 77.2 percent nickel, 4.8 percent copper,1.5 percent chromium and 14.9 percent iron), Monel, copper, silver,bismuth, and alloys thereof. For examp-ile, lead-tin, lead-bismuth, andtin-bismuth alloys may be employed.

It has been found that when a cathode in a phosphine producing cell ismade a contact electrode, in accordance with the invention, the reactivematerial contacts the cathode more efliciently forming reservoirs ofphosphorus disclosed herein and allow a phosphine cell to remain inoperation for longer periods of time than previously realized.

FIGURES 4-12 illustrate various modified contact electrodes which may beemployed in the practice of the invention. FIGURE 3 illustrates thepreferred contact electrode of the invention. The edges 46 and grooves48 of these electrodes may be formed by machining, pressing, bending,rolling, soldering sheets or rods together, or casting the contactelectrode to a desired shape.

FIGURES 3-7 illustrate contact electrodes which have been machinepressed, machined, or cast. FIGURE 8 illustrates a fiat sheet of metalwhich has been bent into the desired shape to provide sharp edges.FIGURE 9 illustrates a plurality of bars soldered together while FIG-URE 10 illustrates a group of octagonal rods in close proximity to oneanother held together by known means. FIGURE 11 illustrates a groupingof short cylindrical discs soldered to a base plate. FIGURE 12illustrates circular orifices in a base plate which provides sharp edges46. Suitable results may be achieved with a contact electrode havingbetween about 2 and 55 inches of sharp edges per square inch. It ispreferred that the contact electrode have between about 4 and 42 inchesof sharp edges per square inch, but the cell has been found to operatein an efficient manner when the cathode contains between about 10 andinches of sharp edges per square inch. The spacings between the edges 46or the width of the base of each groove 48 may be between about A of aninch and A,; of an inch with a preferred width being between about of aninch and A; of an inch, however, optimum results are achieved utilizingbetween about of an inch and of an inch. Thus the number of grooves perinch on the electrode should be between about eight and thirty-two, withbetween about ten and twenty grooves per inch. being preferred, butoptimum results being obtained utilizing between about fourteen and.

eighteen grooves per inch.

The depth of the groove may vary depending upon the modificationutilized. A depth greater than of an inch yields suitable results. Whenrods or bars are utilized to provide edges, it is the width between eachbar that provides reservoirs for phosphorus as seen in FIGURES 9 and 10.However, the preferred range for the depth of the groove, is betweenabout of an inch and 1 inch, with optimum results being obtained whenthe depth of the groove is between about of an inch and /8 of an inch.

Suitable anode materials include lead, platinum, lead.

peroxide, graphite, and other materials of construction capable ofconducting a current and resisting corrosion under the conditions ofelectrolysis employed, An electrolyte which is non-reactive with moltenphosphorus or the reactive material and which is capable of forminghydrogen ions during electrolysis may be employed as a catholyte andanolyte. Typical examples of suitable compounds in aqueous solution,whichmay be employed as electrolyte include hydrochloric acid, sodiumchloride, lithium chloride, potassium chloride, sodium sulfate,potassium sulfate, monosodium phosphate, disodium phosphate, aceticacid, ammonium hydroxide, phosphoric acid, sulfuric acid, and mixturesthereof. The concentration of the electrolyte may vary between aboutfive and about 90 percent with a concentration of between about 10 and75 percent being preferred, and a concentration of between about 5 andabout 50 percent yielding optimum results.

Improved results have been obtained when metallic ions are present inthe electrolyte in small proportions. For example, ions of metals suchas antimony, bismuth, lead, tin, cadmium, mercury, silver, zinc, cobalt,calcium, barium, and mixtures thereof may be employed. The metal ionsmay be placed in the electrolyte by employing a consumable anode of thedesired metal or metalssuch as a lead anode, whereby metal ions areformed in the electrolyte and transferred to the area adjacent to thecathode. Sal-ts or other compounds of the metals such as chloride,phosphates, acetates and the like may be dissolved in the electrolyte ifdesired. In another embodiment finely divided metal in elemental form isdissolved in the electrolyte. Suflicient metal ion may be added to theelectrolyte to provide a metal ion concentration of between about 0.01and 3.0 percent by weight of the electrolyte, with between about 0.02percentand 0.5 percent by weight of electrolyte being the preferredrange, but between about 0.01 and .5 percent also being a suitablerange.

During electrolysis the temperature of the catholyte and anoly-te shouldbe maintained above the melting point of phosphorus (about 44centigrade), and below the boiling point of the electrolyte.Temperatures between about 60 centigrade and 110. centigrade aresatisfactory but optimum yields of phosphine are obtained attemperatures between about 70 centigrade and about centigrade I When anelectric current is passed through the cell, molten phosphorus on thesurface of the cathode is consumed in the formation of the catholyte gasin the cathode section. The catholyte gas is predominately phosphine butcontains some hydrogen. The anolyte gas depends on the over voltages ofthe anions and the anolyte with reference to the anode material. Thus,for example, the anolyte gas predominates in oxygen if sulfuric acid orphosphoric acid is used with a platinum anode, whereas for the sameanode, chlorine predominatesif hydrochloric acid is used as the anolyte.Thus, the co-productionof anionic oxidation products may be carried outin the anode compartment of the cell of this invention without departingfrom the spirit of the invention.

As phosphorus is consumed on the surface of the cathode to yieldphosphine, additional phosphorus passes from the molten pool of reactivematerial, phosphorus, to the vertical cathodic surface. The currentdensity on the cathode may be controlled so that the grooves between theedges act, as a reservoir for phosphorus. phosphorus is consumed at thepart of the reservoir in contact with the electrolyte, it is readilyreplaced from the extra supply in the reservoir. The consumed phosphorusthen being replenished on vthe cathode surface continuously from themolten pool of phosphorus or other reactive material. The cathodiccurrent density may be 'set by the operator and is dependent on whichdensity gives the best results, the celldesign and the construction ofthe cathode.

The phosphine containing gas produced at the cathode has a relativelyhigh concentration of phosphine, usually more than sixty percent, and itmay be as high as ninety percent phosphine by volumeor higher. Thecatholyte gas is substantially free from other phosphorus hydrides.

In one embodiment of the invention, a lead plate containing machinedgrooves and a graphite rod are employed as the cathode and anode,respectively. Under these conditions it is found that the wicking effectof the cathode is markedly improved. In carrying out the process of theinvention, it was observed that a wicking action occurred at the cathodeprior to energizing the cell, that is, the thin layer of moltenphosphorus formed on the outer surface of the vertical cathode. abovethe level of the molten pool of phosphorus before any current wasimpressed upon this system. As soon as the current was caused to flow,the wicking action became rapid, occurring substantially over the entiresurface of the cathode. The thin layer of phosphorus contacting thecathode was maintained continuous over a period of six months withoutany formation of spongy masses. The rate of the wicking action wasfaster with some metals than with others, and the thickness of thephosphorus layer on the metal surfaces was thicker on some metals thanon others. Although in the-description of the invention a plate-likecathode is illustrated, it is to be understood that grooved Thus, as

rods or cylindrical shape cathodes are also within the scope of theinvention.

Suitable reactive materials which may be utilized in the practice ofthis invention are sulfur; the alkali metals, e.g., potassium, sodium,lithium, rubidium, and cesium; the alkaline earth metals, e.g.,beryllium, calcium, strontium, barium, as well as magnesium, andgermanium; and lead.

The diaphragm may or may not be coated as illustrated in FIGURE 1.However, in the preferred embodiment of the invention, whereasphosphorus is the reactive material, a coating of glass fabric givesbeneficial results.

The following examples are presented to further define the inventionwithout any intent of being limited thereby. All parts are by weight andall temperatures are in degrees centigrade unless otherm'se specified.

Example 1 A lead cathode was placed in an electrolytic cell. This leadplate had protrusions covering its surface which measured x of an inchacross its top and was A; of an inch deep. The distance between eachprotrusion was of an inch. These protrusions were on only one surface ofthe lead plate and were formed by amultiplicity of longitudinal andhorizontal grooves as illustrated in FIGURE 4. A- graphite anodesurrounded by a porcelain diaphragm was also placed in the cell. Anelectrolyte of six percent hydrochloric acid plus 0.05 percent lead wasutilized as the anolyte and the catholyte electrolyte. This electrolytemixture was maintained at 85 centigrade. Molten yellow phosphorus wasadmitted to the cell so that the bottom of the contact electrode(cathode) was in contact with the phosphorus. It was observed that the'phosphorus climbed up the cathode and completely cov- Example 2 Aporous lead plate having smooth surfaces on both sides was'utilized asthe cathode in the electrolytic cell. In all other respects theapparatus was similar to that of Example 1, except five percenthydrochloric acid containing 1.5 grams per liter of lead chloride wasutilized as the electrolyte. A cathodic current density of 24 amperesper square foot was maintained for a period of 17 days. The cell wasshut down when the spongy deposits, which appeared on the surface of thecathode, began to decrease the efiiciency of the cell. During theoperation of this cell the cathode gas was found to contain betweenabout 85 to 86 percent phosphine.

Example 3 The apparatus of Example 1 was again utilized, except that thecontact electrode (cathode) contained protrusions on both sides A of aninch square x /s of an inch deep arranged so as to form grooves ,4 of aninch wide and an electrolyte comprisingten percent hydrochloric acid and0.04 percent lead was utilized. The current density was maintained at 32amperes per square foot. After sixty-six days of continuous operationthe cell was shut down and the cathode examined.

The cathode showed no evidence of a spongy mass or failure of thephosphorus layer. During the operation of the cell from 82 to 86 percentphosphine was found in the phosphine gas.

Example 4 The electrolytic cell of Example 1 was again utilized.

' inch deep throughout its length. The grooves were of an inch wide. Acurrent density of 30 amperes per square foot was applied to the cathodefor a period of 21 days. After this period of time no failure of thephosphorus film was experienced. On a visual inspection of the cathodeno spongy masses were found. During the operation of the cell betweenand 92 percent of the cathode gas was phosphine.

It will be recognized by those skilled in the art that variousmodifications within the invention are possible, some of which arereferred to above. Therefore, the above description should not belimiting, except as defined by the appended claims.

What is claimed is:

1. process for preparing phosphine which comprises contactin phosphoruswith a cathode containing a plurality of sharp-edged longitudinalgrooves on its surface, whereby the phosphorus climbs up andsubstantially contacts the entire surface of the cathode, andmaintaining an electrical current through said cathode in the'presenceof an anode, a diaphragm and an electrolyte so that phosphine isproduced, and recovering phosphine from the catholyte gas evolved.

2. A process in accordance with claim 1 wherein the cathode containsbetween about eight and thirty-two grooves per inch of cathode surface.

3. A process in accordance with claim 1 wherein the cathode contains aseries of protrusions.

4. A process in accordance with claim 1 wherein the cathode contains aseries of horizontal and vertical grooves.

References Cited by the Examiner UNITED STATES PATENTS 1,771,091 7/ 1930Lawaczeck 204283 2,025,674 12/1935 Schweitzer 204289 3,085,967 4/1963Motock 204284 3,109,788 11/1963 Miller et al. 204-101 3,109,791 11/1963Gordon 204101 JOHN H. MACK, Primary Examiner. MURRAY A. TILLMAN,Examiner.

L. G. WISE, H. M. FLOURNOY, Assistant Examiners.

1. A PROCESS FOR PREPARING PHOSPHINE WHICH COMPRISES CONTACTINGPHOSPHORUS WITH A CATHODE CONTAINING A PLURALITY OF SHARP-EDGEDLONGITUDINAL GROOVES ON ITS SURFACE, WHEREBY THE PHOSPHORUS CLIMBS UPAND SUBSTANTIALLY CONTACTS THE ENTIRE SURFACE OF THE CATHODE, ANDMAINTAINING AN ELECTRICAL CURRENT THROUGH SAID CATHODE IN THE PRESENCEOF AN ANODE, A DIAPHRAGM AND AN ELECTROLYTE SO THAT PHOSPHINE ISPRODUCED, AND RECOVERING PHOSPHINE FROM THE CATHOLYTE GAS EVOLVED.